It is already generally known that relatively brittle mill feed materials, such as for example cement raw materials, cement clinker, ore material, coal and the like, can be comminuted particularly economically or with a saving of energy in a so-called material bed roll mill in which two grinding rolls which can be driven in rotation in opposite directions are pressed against one another with a relatively high pressure (cf. for example Walter Duda, Cement-Data-Book, Vol. 1, 3rd edition, 1985, pages 255 to 261).
Since the outer circumferential roll surfaces are subjected to very high stresses both with regard to abrasion (wear) and also with regard to pressures, especially in the case of the aforementioned brittle and abrasive mill feed materials, the tire of each grinding roll is produced from particularly wear-resistant material. These roll materials include chilled cast iron as well as alloyed hard materials which are applied by build-up welding onto the roll base material. Nevertheless when comminution occurs in a material bed roll mill the high pressures acting on the roll surfaces or roll tires have the effect that, after a period of time, the roll material, particularly the build-up welded roll tires usually used nowadays, becomes fatigued particularly in the region near the surface, in addition to the sometimes considerable wear. This material fatigue limits the service life of these grinding rolls so that the roll tires can no longer be reused.
In EP-B-0 563 564 a material bed roll mill is proposed in which grinding rolls have a tire made from a wear-resistant chilled cast iron, which may for example be inter alia a highly wear-resistant bainitic cast material. The special feature of these known grinding rolls is that profilings in the form of weld beads made from wear-resistant build-up welding material are applied to the surface of the chilled cast iron tire of each grinding roll. It has in fact been shown that, by constructing the grinding rolls from chilled cast iron with build-up welds, a markedly higher compression strength and thus a longer service life with regard to wear can be achieved by comparison with the build-up welded grinding rolls mentioned above. In providing these known grinding rolls with a tire made from chilled cast iron, however, the chilled cast iron or chilled cast material has a relatively brittle behaviour. In the case of relatively pulsating or striking comminution work or stress, such as is frequently the case with very brittle mill feed materials in large lumps, this can lead to spontaneous fracture of the chilled cast material. Moreover, unwanted fractures can even occur during the production of the grinding rolls; that can occur due to the contraction strains occurring when the tire is being shrink-fitted onto the basic roll body.
The object of the invention, therefore, is to improve the known method referred to above in such a way that, while maintaining a relatively high wear resistance and compression strength, a particularly high operational reliability of the roll tire (and thus of the entire grinding roll) in relation to fractures can be achieved.